Image projection apparatus

ABSTRACT

The image projection apparatus includes an exhaust air outlet through which an exhaust air flows out from an inside of the apparatus to an outside thereof, an air inlet through which an external air flows in from the outside of the apparatus to the inside thereof, a temperature detector that detects a temperature of the external air flowing into the inside of the apparatus through the air inlet, and a controller that performs a protection operation when one of a predetermined temperature corresponding to a temperature of the exhaust air and a predetermined temperature change caused by flowing in of the exhaust air through the air inlet is detected by the temperature detector. The apparatus enables quick detection of a state in which the exhaust air outlet is blocked to perform the protection operation.

CROSS-REFERENCE

This is a continuation of application Ser. No. 12/187,045 filed 8 Aug.2008, the entire disclosure of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to an image projection apparatus such as aliquid crystal projector, and more particularly to an air exhaustingstructure of the image projection apparatus.

The image projection apparatus (hereinafter referred to as projector)has an air exhausting structure, which forcibly exhausts air that hascooled a light source lamp or other heat generating devices (orexothermic devices) to the outside with a fan. However, when theprojector is used in a state in which an exhaust air outlet of theprojector is placed near an obstacle such as a wall (that is, in a statein which the exhaust air outlet is blocked), the cooling of the heatgenerating devices is obstructed, and this may cause trouble in theoperation of the projector. Therefore, many projectors include atemperature sensor thereinside and have a protection function to warn auser or to turn off the light source lamp when an abnormal temperatureincrease is detected.

Japanese Patent Laid-Open No. 2002-258238 discloses a projector in whichplural temperature sensors are provided thereinside to monitor thetemperatures of respective portions inside the projector. Further,Japanese Patent Laid-Open No. 2003-043577 discloses a projector whichincludes a temperature sensor for detecting the temperature of anexternal air and another temperature sensor for detecting thetemperature in the vicinity of the light source lamp, and turns off thelight source lamp when the difference between the temperatures detectedby these temperature sensors becomes large.

However, when the projectors disclosed in aforementioned Japanese PatentLaid-Open Nos. 2002-258238 and 2003-043577 are used in the state inwhich the exhaust air outlet is blocked, the temperature of the airaround the light source lamp initially increases. Afterwards, a lampcase which is a heat insulating member surrounding the light source lampis heated, and then a temperature increase is detected by thetemperature sensor after the heat transmits to the air around the lampcase from it. In other words, the temperature increase of the lightsource lamp is detected after the heat transmits to the lamp case andthe air therearound, so that the state in which the exhaust air outletis blocked cannot be detected quickly.

A temperature sensor may be provided inside the lamp case. However, thetemperature inside of the lamp case increases even under a normal usagecondition. Therefore, a mechanical sensor using a bimetal is commonlyused as the temperature sensor provided inside of lamp case.Furthermore, the mechanical sensor is used to forcibly turn off thelight source lamp for final protection thereof, and it is not easy for auser to recover the projector from the state in which the mechanicalsensor has been activated.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an image projection apparatus capable ofquickly detecting a state in which an exhaust air outlet is blocked andbeing easily recovered from a state in which a protection operation hasbeen performed.

The present invention provides, according to an aspect thereof, an imageprojection apparatus that projects an image using light from a lightsource. The apparatus includes an exhaust air outlet through which anexhaust air flows out from an inside of the apparatus to an outsidethereof, an air inlet through which an external air flows in from theoutside of the apparatus to the inside thereof, a temperature detectorwhich detects a temperature of the external air flowing into the insideof the apparatus through the air inlet, and a controller which performsa protection operation when one of a predetermined temperaturecorresponding to a temperature of the exhaust air and a predeterminedtemperature change caused by flowing in of the exhaust air through theair inlet is detected by the temperature detector.

Other aspects of the present invention will be apparent from theembodiments described below with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the air exhaust and intakestructure around a lamp in a projector, which is a first embodiment(Embodiment 1) of the present invention.

FIG. 2 is a sectional view showing the air exhaust and intake structurein Embodiment 1.

FIG. 3 is a sectional view showing airflows in the air exhaust andintake structure in Embodiment 1.

FIG. 4 is a graph diagram showing changes in temperature detected by atemperature sensor in the projector of Embodiment 1 and in aconventional projector.

FIG. 5 is a sectional view showing a modified example of the air exhaustand intake structure in Embodiment 1.

FIG. 6 is a sectional view showing the air exhaust and intake structurein a second embodiment (Embodiment 2) of the present invention.

FIG. 7 is an exploded perspective view showing the projector ofEmbodiment 1.

FIG. 8 is a plane view showing cooling airflows in the projector ofEmbodiment 1.

FIG. 9 is a flowchart showing a protection operation process inEmbodiment 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowwith reference to the accompanied drawings.

(Overall configuration of projector)

FIG. 7 shows the configuration of a liquid crystal projector (imageprojection apparatus) that is a first embodiment (Embodiment 1) of thepresent invention.

In this figure, reference numeral 1 denotes a light source lamp(hereinafter referred to simply as “lamp”), which is an ultrahigh-pressure mercury discharge lamp in this embodiment. However,discharge lamps other than the ultra high-pressure mercury dischargelamp may be used as the lamp 1, such as a halogen lamp, a xenon lamp,and a metal halide lamp.

Reference numeral 2 denotes a lamp holder which holds the lamp 1, 3 anexplosion-proof glass, and 4 a glass holder. Reference symbol α denotesan illumination optical system which converts light from the lamp 1 intocollimated light with a uniform luminance distribution. Reference symbolβ denotes a color separating/combining optical system. The colorseparating/combining optical system β separates the light from theillumination optical system α into a red (R) light component, a green(G) light component and a blue (B) light component, guides them toliquid crystal panels for R, G, and B, respectively, and then combinesthe light components from the liquid crystal panels.

Reference numeral 5 denotes a projection lens barrel which projects thelight from the color separating/combining optical system β onto aprojection surface such as a screen, not shown. A projection opticalsystem, described later, is housed in the projection lens barrel 5.

Reference numeral 6 denotes an optical box which accommodates the lamp1, the illumination optical system α, and the color separating/combiningoptical system β, and to which the projection lens barrel 5 is fixed.The optical box 6 has a lamp case portion (hereinafter referred tosimply as lamp case) 6 a formed thereon, which surrounds the lamp 1.

Reference numeral 7 denotes an optical box lid which covers the opticalbox 6 accommodating the illumination optical system α and the colorseparating/combining optical system β. Reference numeral 8 denotes a PFC(Power Factor Correction) power supply board which generates DC powerfor each of circuit boards from a commercial power supply. Referencenumeral 9 denotes a power supply filter board, and 10 a ballast powersupply board which drives (lights) the lamp 1 together with the PFCpower supply board 8.

Reference numeral 11 denotes a control board which drives the liquidcrystal panels and controls lighting of the lamp 1 with power from thePFC power supply board 8.

Reference numerals 12A and 12B denote first and second optical systemcooling fans, respectively, which take in air through an air inlet 21 aformed in a lower exterior case 21, later described, to cool opticalelements such as the liquid crystal panels and polarizing platesprovided in the color separating/combining optical system β.

Reference numeral 13 denotes a first RGB duct which guides the coolingairflows from the first and second optical system cooling fans 12A and12B to the optical elements in the color separating/combining opticalsystem β.

Reference numeral 14 denotes a lamp cooling fan which sends a blowingairflow to the lamp 1 to cool it. Reference numeral 15 denotes a firstlamp duct which holds the lamp cooling fan 14 and guides the coolingairflow to the lamp 1. Reference numeral 16 denotes a second lamp ductwhich holds the lamp cooling fan 14 and forms the duct together with thefirst lamp duct 15.

Reference numeral 17 denotes a power supply cooling fan which takes inair through an air inlet 21 b formed in the lower exterior case 21 tocirculate a cooling airflow within the PFC power supply board 8 and theballast power supply board 10 to cool them. Reference numeral 18 denotesan exhaust fan which exhausts air that has been provided from the lampcooling fan 14 to the lamp 1 and whose temperature is increased bycooling the lamp 1 through an exhaust air outlet 24 a formed in a secondside plate 24, later described.

The lower exterior case 21 accommodates the lamp 1, the optical box 6,the power supply system boards 8 to 10, the control board 11 and thelike.

Reference numeral 22 denotes an upper exterior case which covers thelower exterior case 21 accommodating the optical box 6 and the like.Reference numeral 23 denotes a first side plate which covers sideopenings formed by the cases 21 and 22 together with the second sideplate 24. The lower exterior case 21 has the abovedescribed air inlets21 a and 21 b formed therein, and the side plate 24 has the exhaust airoutlet 24 a and an air inlet 24 b formed therein. The lower exteriorcase 21, the upper exterior case 22, the first side plate 23 and thesecond side plate 24 constitute a chassis (case) of the projector.

Reference numeral 25 denotes an interface board on which connectors forreceiving various signals are mounted, and 26 an interface reinforcementplate attached to the inside face of the first side plate 23.

Reference numeral 27 denotes an exhaust duct which guides a heatedexhaust air from the lamp 1 to the exhaust fan 18 to prevent diffusionof the exhaust air in the chassis.

Reference numeral 28 denotes a lamp lid. The lamp lid 28 is removablyprovided on the bottom of the lower exterior case 21 and is fixedthereto by screws, not shown. Reference numeral 29 denotes a setadjustment leg. The set adjustment leg 29 is fixed to the lower exteriorcase 21, and the height of its leg 29 a is adjustable. The adjustment ofthe height of the leg 29 a enables adjustment of an inclination angle ofthe projector.

Reference numeral 30 denotes an RGB air intake plate which holds afilter, not shown, attached to the outside of the air inlet 21 a formedin the lower exterior case 21.

Reference numeral 31 denotes a prism base which holds the colorseparating/combining optical system R. Reference numeral 32 denotes abox side cover which has duct-shaped portions for guiding the coolingairflows from the first and second optical system cooling fans 12A and12B for cooling the optical elements and the liquid crystal panels inthe color separating/combining optical system β. Reference numeral 33denotes a second RGB duct which forms the duct together with the boxside cover 32.

Reference numeral 34 denotes an RGB board to which flexible boardsextending from the liquid crystal panels disposed in the colorseparating/combining optical system β are connected and which isconnected to the control board 11.

Reference numeral 35 denotes an RGB cover which prevents electricalnoise from entering the RGB board.

(Cooling Structure)

Next, the cooling structure in the projector of the present embodimentwill be explained with reference to FIG. 8. As described above, thisprojector accommodates therein five fans 12A, 12B, 14, 17, and 18 forflowing airs in plural airflow paths described below to cool theirrespective cooling targets.

In an airflow path B indicated by solid-line arrows in FIG. 8, an airsucked into the chassis by the lamp cooling fan 14 is fed as a coolingair through the ducts 15 and 16 to the lamp 1. The airflow having cooledthe lamp 1 is guided into the exhaust duct 27 to be exhausted to theoutside of the chassis by the exhaust fan 18.

In an airflow path A indicated by dotted-line arrows in FIG. 8, an airsucked by the first and second cooling fans 12A and 12B from the outsideof the chassis flows into the airflow path A through the air inlet 21 aformed below the projection lens barrel 5. The second cooling fan 12B isdisposed below the projection lens barrel 5.

A cooling air formed by this air cools the optical elements in thecolor-separating/combining optical system β housed inside the opticalbox 6. Most of this cooling air flows toward the PFC power supply board8 and the ballast power supply board 10 adjacent to the optical box 6 tocool the electrical devices mounted on these boards 8 and 10. Afterthat, the cooling air is exhausted to the outside of the chassis by theexhaust fan 18 and the power supply cooling fan 17.

In an airflow path C indicated by one-dot-chain-line arrows in FIG. 8,an air sucked through the air inlet 21 b (not shown in FIG. 8) formed inthe lower exterior case 21 flows into the airflow path C. A cooling airformed by this air is guided toward the ballast power supply board 10and the PFC power supply board 8 together with an air inside the chassisby a sucking force of the power supply cooling fan 17 or the exhaust fan18. After cooling these boards 8 and 10, the cooling air is exhausted tothe outside of the chassis by the power supply cooling fan 17 and theexhaust fan 18.

The air exhaust and intake structure around the lamp 1 in theabovedescribed cooling structure will be explained in detail withreference to FIGS. 1 and 2. FIG. 2 shows a cross-sectional view of thelamp case 6 a and the exhaust duct 27 shown in FIG. 1.

A lamp unit 101, constituted by the lamp 1 as a heat generating memberand the lamp holder 2 which holds the lamp 1, is housed in the inside ofthe lamp case 6 a which is the lamp-housing member as a heat insulatingmember. An opening for exhausting heat is formed in the lamp case 6 a,and it is connected to an opening (inflow opening) formed in the exhaustduct 27. Another opening (outflow opening) formed in the exhaust duct 27is formed so as to face an air intake plane of the exhaust fan 18.

Thereby, an air in the lamp case 6 a passes through the inside of theexhaust duct 27 and reaches the exhaust fan 18, and then is exhausted tothe outside through the exhaust air outlet 24 a formed in the downstreamside from the exhaust fan 18. As described above, the exhaust air outlet24 a is formed in the second side plate 24 which constitutes part of theexterior surface of the projector.

In such a configuration, since the lamp 1 generates much heat in itslighting state, the inside of the lamp case 6 a becomes a hightemperature of nearly 200° C. Therefore, the exhausted air from theexhaust air outlet 24 a becomes a high temperature even if a coldexternal air is mixed with the hot air after having cooled the lamp 1.

A main airflow W1, from the lamp unit 101 until being exhausted to theoutside of the projector, flows through the abovementioned airflow pathB. In addition to this, an airflow path to generate a sub airflow W2 isformed in the present embodiment. The configuration to form the airflowpath for the sub airflow W2 will be explained below.

At first, the air inlet 24 b is provided at the position adjacent to (inthe vicinity of) the exhaust air outlet 24 a on the second side plate24. In other words, the air inlet 24 b and the exhaust air outlet 24 aare provided on the same surface (second side plate 24) of pluralexterior surfaces (upper, lower and four side exterior surfaces) of theprojector. Hereinafter, the exterior surface where the exhaust airoutlet 24 a (and the air inlet 24 b) is provided is referred to simplyas exhaust surface of the projector.

Further, in the vicinity of the connecting portion of the exhaust fan 18and the exhaust duct 27, an aperture (gap) H1 is formed to form anairflow from the peripheral region of the lamp case 6 a to the exhaustfan 18.

In such a configuration, when the exhaust fan 18 is driven, a negativepressure is created on an intake side of the exhaust fan 18, and theairflow W1 passing through the inside of the lamp case 6 a and theairflow W2 passing through an outer peripheral region of the lamp case 6a are formed.

Inside the lamp case 6 a, a first temperature sensor S1 is providedwhich detects a temperature inside the lamp case 6 a. A secondtemperature sensor S2 which detects a temperature (ambient temperature)of an air (external air) flowing in through the air inlet 24 b formed inthe second side plate 24 is provided in a region in the vicinity of theair inlet 24 b (region facing an outer surface of the lamp case 6 a andthe air inlet 24 b). The second temperature sensor S2 corresponds to a“temperature detector”, and the first temperature sensor S1 correspondsto “another temperature detector”.

In a state in which the exhaust air outlet 24 a is not covered (blocked)by an obstacle which will be described later, the second temperaturesensor S2 can detect a temperature equivalent to an external airtemperature (for example, a temperature in a room in which the projectoris installed) even though it is disposed in the vicinity of the lampcase 6 a.

The first temperature sensor S1 is a mechanical sensor which uses abimetal and the like to be able to protect the lamp 1 even if othertemperature sensors including the second temperature sensor S2 breakdown. Also, the first temperature sensor S1 has a function to block anelectric current which lights the lamp 1 in a case where the temperaturedetected by the first temperature sensor S1 exceeds a certaintemperature (temperature higher than detection temperature ranges of theother temperature sensors).

In contrast, the second temperature sensor S2 is a temperature sensorthat uses an IC element, and outputs an electrical signal indicating thedetected temperature. Therefore, electrical control based on the outputof the second temperature sensor S2 can be performed.

FIG. 3 shows the state in which the projector is placed with the exhaustsurface being close to an obstacle (external object) WL such as anindoor wall. Hereinafter, such a state is referred to as “state in whichthe exhaust surface (exhaust air outlet 24 a) is blocked”.

In this state, the progress of an air W1 a exhausted to the outsidethrough the exhaust air outlet 24 a is blocked by the obstacle WL, andthus the air W1 a spreads out as shown by arrows Wb along the obstacleWL.

As described above, the negative pressure is created on the intake sideof the exhaust fan 18. Therefore, a negative pressure is generated alsoinside of the air inlet 24 b formed adjacent to the exhaust fan 18 andthe exhaust air outlet 24 a. Thus, an air W2 c that is part of theexhausted air flows into the inside of the projector (chassis) throughthe air inlet 24 b. The air W2 c that has flowed into the inside of theprojector is drawn by the exhaust fan 18 and returns (W2 d) to theintake side of the exhaust fan 18. In this manner, in the state in whichthe exhaust surface is blocked, an exhaust airflow closed loop (W1a˜Wb˜W2 c˜W2 d˜W1 a) is formed in which the air exhausted from theexhaust air outlet 24 a is taken in again though the air inlet 24 b.

As a result, the second temperature sensor S2 can detect the temperatureof the exhausted air W2 c that has flowed into the inside of theprojector through the air inlet 24 b. In other words, the exhaustairflow closed loop described above is instantly formed when the exhaustsurface is blocked. Therefore, the temperature of the exhausted air thathas flowed into the inside of the projector can be quickly (sensitively)detected by the second temperature sensor S2, and thereby, as will bedescribed later, a user can be quickly alerted about the state in whichthe exhaust surface is blocked.

FIG. 4 shows the results of experiments performed using a projectoremploying the abovedescribed configuration and a conventional projectornot employing the abovedescribed configuration. A dash-dot line graphshows a change in temperature detected by a temperature sensor providedoutside of the lamp case and in its vicinity in a conventional projectorwhich is not equipped with an air inlet at a position adjacent to anexhaust air outlet. A solid line graph shows a change in temperaturedetected by the second temperature sensor S2 in the projector of thepresent embodiment in which the air inlet 24 b is formed adjacent to theexhaust air outlet 24 a. Both projectors were set in the state in whichthe exhaust surface is blocked at a time T1.

In the conventional projector, in a state before the time T1 (normalstate in which the exhaust surface is not blocked), the temperaturedetected by the temperature sensor increased slowly in accordance withthe increase of the temperature around the lamp case 6 a. Then, afterthe time T1, although the temperature detected by the temperature sensorincreased further than that detected before the time T1, the rate of thetemperature increase was not so high.

On the other hand, in the projector of the present embodiment, in thestate before the time T1, since a cold external air is taken in aroundthe lamp case 6 a through the air inlet 24 b, the temperature detectedby the second temperature sensor S2 hardly increased at all. However,immediately after the time T1, the temperature detected by the secondtemperature sensor S2 increased rapidly. Further, the temperatureincreased much higher than in the conventional projector.

As can be understood from the comparison of these graphs, the state inwhich the exhaust surface is blocked can be detected by monitoring thetemperature detected by the second temperature sensor S2 or the changethereof.

The present embodiment uses this fact to perform a protection operationin response to the exhaust surface being blocked, according to aflowchart shown in FIG. 9. This protection operation is executed by aCPU (hereinafter referred to as controller) 11A which is mounted on thecontrol board 11 shown in FIG. 7 according to a computer program storedin the CPU 11A.

In step (abbreviated as S in the figure) 1001, the controller 11Aobtains an output (detected temperature) from the second temperaturesensor S2. Next, in step 1002, the controller 11A determines whether ornot the temperature detected by the second temperature sensor S2 ishigher than a predetermined temperature (that is, whether or not atemperature abnormality is occurring). The predetermined temperature isa temperature corresponding to the temperature of the exhaust airflowing out through the exhaust air outlet 24 a, and it is, for example,Ts2 (a temperature of around 65° C.) shown in FIG. 4.

The predetermined temperature Ts2 is a particular temperature detectedby the second temperature sensor S2 in the state in which the exhaustsurface is blocked. Therefore, detecting the predetermined temperatureTs2 enables an accurate determination of the state in which the exhaustsurface is blocked.

The “temperature corresponding to the temperature of the exhaust air”includes the same temperature as that of the exhaust air and othertemperatures such as an average temperature or a minimum temperature ofthe temperatures detected by the second temperature sensor S2 when theexhaust air flows into the inside of the projector through the air inlet24 b in experiments under various conditions.

Further, the predetermined temperature Ts2 is set lower than atemperature Ts1 at which the lamp 1 is turned off by the controller 11Ain response to an operation of the first temperature sensor S1. In otherwords, the temperature Ts1 and the predetermined temperature Ts2 satisfythe relationship of: Ts1>Ts2.

Thereby, the temperature abnormality can be detected by using the secondtemperature sensor S2 prior to the detection thereof by the firsttemperature sensor S1.

When the temperature abnormality is not occurring in step 1002, theprocess returns to step 1001. On the other hand, when the temperatureabnormality is occurring, the process advances to step 1003 where thecontroller 11A performs a first protection operation. In the firstprotection operation, the controller 11A displays a warning on a displaypart (not shown) which is provided on the upper exterior case 22 orgenerates a warning sound to inform the user of the temperatureabnormality occurring due to the state in which the exhaust surface isblocked.

Next, in step 1004, the controller 11A performs a second protectionoperation. In the second protection operation, the controller 11Aincreases a rotating speed of the exhaust fan 18.

Next, in step 1005, the controller 11A obtains the output of the secondtemperature sensor S2 again. Then, the controller 11A again determineswhether or not the temperature detected by the second temperature sensorS2 is higher than the abovedescribed predetermined temperature (that is,whether or no the temperature abnormality is occurring).

If the temperature abnormality has been resolved and thus thetemperature abnormality is not occurring, the process returns to step1001. On the other hand, if the temperature abnormality is occurring,the process advances to step 1006 where the controller 11A performs athird protection operation. In the third protection operation, thecontroller 11A turns off the lamp 1, and thus the process is finished.

In steps 1002 and 1005, the controller 11A may determine the presence orabsence of a predetermined temperature change (a predetermined rate ofthe temperature increase per unit of time) which is shown by ΔTmp inFIG. 4 and caused by flowing in of the exhaust air through the air inlet24 b.

The predetermined temperature change ΔTmp is a particular temperatureincrease rate generated in the state in which the exhaust surface isblocked, so that detecting the predetermined temperature change ΔTmpenables an accurate determination of the state in which the exhaustsurface is blocked.

The first temperature sensor S1 may be a temperature sensor using an ICelement like the second temperature sensor S2. In this case, thetemperature abnormality can be detected more sensitively by evaluatingthe product of the temperatures detected by both temperature sensors S1and S2.

Note that it is not necessarily needed to perform all of the first tothird protection operations. That is, it is only necessary to perform atleast one of displaying the warning, generating the warning sound,turning off the lamp 1, and increasing the rotating speed of the exhaustfan 18.

Further, the present embodiment described the case where the air inlet24 b and the exhaust air outlet 24 a are provided on the same exteriorsurface. However, as shown in FIG. 5, the air inlet 24 b may be providedclose to the exhaust air outlet 24 a on an exterior surface (backsurface of the lower exterior case 21) adjacent to the exhaust surfaceon which the exhaust air outlet 24 a is provided. Even in this case,since an exhaust airflow closed loop (W1 a˜Wb˜W2 c˜W2 d˜W1 a) is formedin the state in which the exhaust surface is blocked, the same effect asthat of the abovedescribed embodiment can be obtained.

Embodiment 2

FIG. 6 shows the air exhaust and intake structure around the lamp in aliquid crystal projector which is a second embodiment (Embodiment 2) ofthe present invention.

Embodiment 1 described the case where the second temperature sensor S2is placed in the vicinity of the air inlet 24 b. However, the secondtemperature sensor S2 may be placed at a position which will beexplained below together with using an air-guiding member which will beexplained below.

In the present embodiment, the air inlet 24 b is provided near theexhaust air outlet 24 a on an exterior surface (back surface of thelower exterior case 21) adjacent to the exhaust surface on which theexhaust air outlet 24 a is provided. The air-guiding member 201 having aduct shape connects from the air inlet 24 b and an intake surface of theexhaust fan 18. Furthermore, the second temperature sensor S2 is placedinside of an airflow path surrounded by the air-guiding member 201.

The air-guiding member 201 reliably guides an air W2 c flowing thereintothrough the air inlet 24 b to the second temperature sensor S2 in thestate in which the exhaust surface is blocked by the obstacle WL and anexhaust airflow closed loop (W1 a˜Wb˜W2 c˜W2 d˜W1 a) is formed, in thesame manner as in Embodiment 1 (FIG. 6). Therefore, in comparison withEmbodiment 1, the second temperature sensor S2 can be placed at aposition away from the air inlet 24 b. In other words, the degree offreedom in placing the second temperature sensor S2 is improved.

Further, since an independent airflow path for the air W2 c configuringthe exhaust airflow closed loop can be formed inside the projector byproviding the air-guiding member 201, the blocking of the exhaustsurface can be detected more sensitively.

The control of the protection operation using the second temperaturesensor S2 is the same as that in Embodiment 1.

According to each of the abovedescribed embodiments, the predeterminedtemperature corresponding to the exhaust air flowing into the apparatusthrough the air inlet or the predetermined temperature change caused bythe flowing in of the exhaust air through the air inlet in the state inwhich the exhaust air outlet is blocked can be sensitively detected withthe second temperature sensor S2. Thereby, the protection operation canbe performed before an excessive temperature increase inside of theprojector occurs. Therefore, deterioration in lifetime of the lamp ordamage due to heating of heat-vulnerable components such as opticalelements can be avoided.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

For example, the above embodiments described the configuration of theair exhaust part for the air that has cooled the lamp. However, asimilar configuration may be employed in an air exhaust part for an airthat has cooled a heat-generating device other than the lamp, such asthe air exhaust parts in the airflow paths A and C shown in FIG. 8.

Further, for the projector, a transmissive liquid crystal panel and adigital micromirror device (DMD) may be used instead of the reflectiveliquid crystal panel.

This application claims the benefit of Japanese Patent Application No.2007-204920, filed on 7 Aug. 2007, which is herein incorporated byreference in its entirety.

1. An image projection apparatus projecting an image using light from alight source, the image projection apparatus comprising: an exhaust airoutlet through which an exhaust air flows out from an inside of theapparatus to an outside thereof; an air inlet through which an externalair flows in from the outside of the apparatus to the inside thereof; atemperature detector that detects a temperature of the external airflowing into the inside of the apparatus through the air inlet; and acontroller that performs a protection operation when one of atemperature being higher than a predetermined temperature correspondingto a temperature of the exhaust air or a temperature change being largerthan a predetermined temperature change caused by flowing in of theexhaust air through the air inlet is detected by the temperaturedetector.
 2. An image projection apparatus according to claim 1, whereinthe apparatus includes plural exterior surfaces, and the exhaust airoutlet and the air inlet are provided on a same surface of the pluralexterior surfaces.
 3. An image projection apparatus according to claim1, wherein the apparatus includes plural exterior surfaces, and theexhaust air outlet and the air inlet are provided on surfaces adjacentto each other of the plural exterior surfaces.
 4. An image projectionapparatus according to claim 1, further comprising an airflow path whichguides the external air that has flowed into the inside of the apparatusthrough the air inlet to the exhaust air outlet.
 5. An image projectionapparatus according to claim 4, further comprising: an air-guidingmember surrounding the airflow path, wherein the temperature detector isdisposed inside of the air-guiding member.
 6. An image projectionapparatus according to claim 1, wherein: the exhaust air that has cooledthe light source flows out from the exhaust air outlet, and thetemperature detector is provided in a region facing an outer surface ofa housing member that houses the light source and the air inlet.
 7. Animage projection apparatus according to claim 6, wherein: thetemperature detector is provided to detect the predetermined temperaturecorresponding to the temperature of the exhaust air, and the apparatusfurther includes another temperature detector that operates at atemperature higher than the predetermined temperature.
 8. An imageprojection apparatus according to claim 1, wherein the protectionoperation includes at least one of displaying a warning, generating awarning sound, turning off the light source, and increasing a rotatingspeed of a fan used for cooling the apparatus.